In the production process of semiconductor integrated circuit devices, after a great number of integrated circuits are formed on a wafer formed of, for example, silicon, each of these integrated circuits is generally subjected to a probe test that basic electrical properties thereof are inspected, thereby sorting defective integrated circuits. This wafer is then cut, thereby forming semiconductor chips. Such semiconductor chips are contained and sealed in respective proper packages. Each of the packaged semiconductor integrated circuit devices is further subjected to a burn-in test that electrical properties thereof are inspected under a high-temperature environment, thereby sorting semiconductor integrated circuit devices having latent defects.
In such electrical inspection of integrated circuits, such as the probe test or the burn-in test, a probe member for electrically connecting each of electrodes to be inspected in an object of inspection to a tester is used. As such a probe member, is known a member composed of a circuit board for inspection, on which inspection electrodes have been formed in accordance with a pattern corresponding to a pattern of electrodes to be inspected, and an anisotropically conductive elastomer sheet arranged on this circuit board for inspection.
As such anisotropically conductive elastomer sheets, those of various structures have heretofore been known. For example, Japanese Patent Application Laid-Open No. 93393/1976 discloses an anisotropically conductive elastomer sheet (hereinafter referred to as “dispersion type anisotropically conductive elastomer sheet”) obtained by uniformly dispersing metal particles in an elastomer, and Japanese Patent Application Laid-Open No. 147772/1978 discloses an anisotropically conductive elastomer sheet (hereinafter referred to as “uneven distribution type anisotropically conductive elastomer sheet”) obtained by unevenly distributing conductive magnetic particles in an elastomer to form a great number of conductive parts extending in a thickness-wise direction thereof and an insulating part for mutually insulating them. Further, Japanese Patent Application Laid-Open No. 250906/1986 discloses an uneven distribution type anisotropically conductive elastomer sheet with which, a difference in level defined between the surface of each conductive part and an insulating part is formed.
In the uneven distribution type anisotropically conductive elastomer sheet, since the conductive parts are formed in accordance with a pattern corresponding to a pattern of electrodes to be inspected of an integrated circuit to be inspected, it is advantageous compared with the dispersion type anisotropically conductive elastomer sheet in that electrical connection between electrodes can be achieved with high reliability even to an integrated circuit small in the arrangement pitch of electrodes to be inspected, i.e., center distance between adjacent electrodes to be inspected.
In such an uneven distribution type anisotropically conductive elastomer sheet, it is necessary to hold and fix it in a particular positional relation to a circuit board for inspection and an object of inspection in an electrically connecting operation to them.
However, the anisotropically conductive elastomer sheet is flexible and easy to be deformed, and so it is low in handling property. In addition, with the miniaturization or high-density wiring of electric products in recent years, integrated circuit devices used therein tend to increase in number of electrodes and arrange electrodes at a high density as the arrangement pitch of the electrodes becomes smaller. Therefore, the positioning and the holding and fixing of the uneven distribution type anisotropically conductive elastomer sheet are going to be difficult upon its electrical connection to electrodes to be inspected of the object of inspection.
In the burn-in test on the other hand, there is a problem that even when the necessary positioning, and holding and fixing of the uneven distribution type anisotropically conductive elastomer sheet to an integrated circuit device has been realized once, positional deviation between conductive parts of the uneven distribution type anisotropically conductive elastomer sheet and electrodes to be inspected of the integrated circuit device occurs when they are subjected to thermal hysteresis by temperature change, since coefficient of thermal expansion is greatly different between a material (for example, silicon) making up the integrated circuit device that is the object of inspection, and a material (for example, silicone rubber) making up the uneven distribution type anisotropically conductive elastomer sheet, as a result, the electrically connected state is changed, and thus the stably connected state is not retained.
In order to solve such a problem, an anisotropically conductive connector composed of a metal-made frame plate having an opening and an anisotropically conductive sheet arranged in the opening of this frame plate and supported at its peripheral edge by an opening edge about the frame plate has been proposed (see Japanese Patent Application Laid-Open No. 40224/1999).
This anisotropically conductive connector is generally produced in the following manner.
As illustrated in FIG. 23, a mold for molding an anisotropically conductive elastomer sheet composed of a top force 80 and a bottom force 85 making a pair therewith is provided, a frame plate 90 having an opening 91 is arranged in alignment in this mold, and a molding material with conductive particles exhibiting magnetism dispersed in a polymeric substance-forming material, which will become an elastic polymeric substance by a curing treatment, is fed into a region including the opening 91 of the frame plate 90 and an opening edge thereabout to form a molding material layer 95. Here, the conductive particles P contained in the molding material layer 95 are in a state dispersed in the molding material layer 95.
Both top force 80 and bottom force 85 in the mold respectively have molding surfaces composed of a plurality of ferromagnetic substance layers 81 or 86 formed in accordance with a pattern corresponding to a pattern of conductive parts of an anisotropically conductive elastomer sheet to be molded and non-magnetic substance layers 82 or 87 formed at other portions than the portions at which the ferromagnetic substance layers 81 or 86 have been respectively formed, and are arranged in such a manner that their corresponding ferromagnetic substance layers 81 and 86 oppose to each other.
A pair of, for example, electromagnets are then arranged on an upper surface of the top force 80 and a lower surface of the bottom force 85, and the electromagnets are operated, thereby applying a magnetic field having higher intensity at portions between ferromagnetic substance layers 81 of the top force 80 and their corresponding ferromagnetic substance layers 86 of the bottom force 85, i.e., portions to become conductive parts, than the other portions, to the molding material layer 95 in the thickness-wise direction of the molding material layer 95. As a result, the conductive particles P dispersed in the molding material layer 95 are gathered at the portions where the magnetic field having the higher intensity is applied in the molding material layer 95, i.e., the portions between the ferromagnetic substance layers 81 of the top force 80 and their corresponding ferromagnetic substance layers 86 of the bottom force 85, and further oriented so as to align in the thickness-wise direction of the molding material layer. In this state, the molding material layer 95 is subjected to a curing treatment, whereby an anisotropically conductive elastomer sheet composed of a plurality of conductive parts, in which the conductive particles P are contained in a state oriented so as to align in the thickness-wise direction, and an insulating part for mutually insulating these conductive parts is molded in a state that its peripheral edge has been supported by the opening edge about the frame plate, thereby producing an anisotropically conductive connector.
According to such an anisotropically conductive connector, it is hard to be deformed and easy to handle because the anisotropically conductive elastomer sheet is supported by the metal-made frame plate, and a positioning mark (for example, a hole) is formed in the frame plate in advance, whereby the positioning and the holding and fixing to an integrated circuit device can be easily conducted upon an electrically connecting operation to the integrated circuit device. In addition, a material low in coefficient of thermal expansion is used as a material for forming the frame plate, whereby the thermal expansion of the anisotropically conductive sheet is restrained by the frame plate, so that positional deviation between the conductive parts of the uneven distribution type anisotropically conductive elastomer sheet and electrodes to be inspected of the integrated circuit device is prevented even when they are subjected to thermal hysteresis by temperature change. As a result, a good electrically connected state can be stably retained.
By the way, in a probe test conducted for integrated circuits formed on a wafer, a method that a wafer is divided into a plurality of areas, in each of which 16 or 32 integrated circuits among a great number of integrated circuits have been formed, a probe test is collectively performed on all the integrated circuits formed in an area, and the probe test is successively performed on the integrated circuits formed in other areas has heretofore been adopted.
In recent years, there has been a demand for collectively performing a probe test on, for example, 64 or 124 integrated circuits, or all integrated circuits among a great number of integrated circuits formed on a wafer for the purpose of improving inspection efficiency and reducing inspection cost.
In a burn-in test on the other hand, it takes a long time to individually conduct electrical inspection of a great number of integrated circuit devices because each integrated circuit device that is an object of inspection is fine, and its handling is inconvenient, whereby inspection cost becomes considerably high. From such reasons, there has been proposed a WLBI (Wafer Lebel Burn-in) test in which the burn-in test is collectively performed on a great number of integrated circuits formed on a wafer in the state of the wafer.
When a wafer that is an object of inspection is of large size of, for example, at least 8 inches in diameter, and the number of electrodes to be inspected formed thereon is, for example, at least 5,000, particularly at least 10,000, however, the following problems are involved when the above-described anisotropically conductive connector is applied as a probe member for the probe test or WLBI test, since a pitch between electrodes to be inspected in each integrated circuit is extremely small.
Namely, in order to inspect a wafer having a diameter of, for example, 8 inches (about 20 cm), it is necessary to use an anisotropically conductive elastomer sheet having a diameter of about 8 inches as an anisotropically conductive connector. However, such an anisotropically conductive elastomer sheet is large in the whole area, but each conductive part is fine, and the area proportion of the surfaces of the conductive parts to the whole surface of the anisotropically conductive elastomer sheet is low. It is therefore extremely difficult to surely produce such an anisotropically conductive elastomer sheet. Accordingly, yield is extremely lowered in the production of the anisotropically conductive elastomer sheet. As a result, the production cost of the anisotropically conductive elastomer sheet increases, and in turn, the inspection cost increases.
When the above-described anisotropically conductive connector is used as a prove member for the probe test or WLBI test of a wafer, the following problems are involved.
In the probe test, the method that a wafer is divided into two or more areas, and the probe test is collectively performed on integrated circuits formed in each of the divided areas is used as described above. When the probe test is performed on integrated circuits formed at a high degree of integration on a wafer having a diameter of 8 inches or 12 inches, it is required to conduct a step of an inspection process in plural times as to one wafer. Accordingly, in order to conduct the probe test on a great number of wafers, the anisotropically conductive elastomer sheet used is required to have high durability in repeated use.
In the WLBI test, on the other hand, the anisotropically conductive elastomer sheet are, at the conductive parts thereof, held with pressure by electrodes to be inspected in a wafer that is an object of inspection and inspection electrodes of the circuit board for inspection, and exposed to a high-temperature environment for a long period of time in this state. Accordingly, the anisotropically conductive elastomer sheet is required to have high durability even when it is used repeatedly under such severe conditions.
From such a point of view, those having durability are selected as materials for the anisotropically conductive elastomer sheet, i.e., an elastic polymeric substance and conductive particles, used in the probe test or WLBI test of a wafer.
Even when those having durability are selected as materials for the anisotropically conductive elastomer sheet, individual products actually obtained often become low in durability. The reason for it is considered to be attributable to the fact that the projected height, the oriented state of the conductive particles, the proportion of the conductive particles, and the like vary in each of the conductive parts of the anisotropically conductive elastomer sheet. As a means for investigating the projected height, the oriented state of the conductive particles, the proportion of the conductive particles, and the like in the respective conductive parts without damaging the anisotropically conductive elastomer sheet, there is nothing other than a means of visual judging. Such means involves a problem that not only objective judgment becomes impossible, but also production cost of the anisotropically conductive elastomer sheet increases because the operation itself is extremely complicated. In addition, since the durability of the anisotropically conductive elastomer sheet cannot be judged by an ordinary conduction test, the degree of the durability is clarified for the first time, in reality, by using the anisotropically conductive elastomer sheet.
The coefficient of linear thermal expansion of a material making up the wafer, for example, silicon is about 3.3×10−6/K. On the other hand, the coefficient of linear thermal expansion of a material making up the anisotropically conductive elastomer sheet, for example, silicone rubber is about 2.2×10−4/K. Accordingly, when a wafer and an anisotropically conductive elastomer sheet each having a diameter of 20 cm at 25° C. are heated from 20° C. to 120° C., a change of the wafer in diameter is only 0.0066 cm in theory, but a change of the anisotropically conductive elastomer sheet in diameter amounts to 0.44 cm.
When a great difference is created between the wafer and the anisotropically conductive elastomer sheet in the absolute quantity of thermal expansion in a plane direction as described above, it is extremely difficult to prevent positional deviation between electrodes to be inspected in the wafer and the conductive parts in the anisotropically conductive elastomer sheet upon the WLBI test even when the peripheral edge of the anisotropically conductive elastomer sheet is fixed by a frame plate having an equivalent coefficient of linear thermal expansion to the coefficient of linear thermal expansion of the wafer.
As probe members for the WLBI test, are known those in which an anisotropically conductive elastomer sheet is fixed on to a circuit board for inspection composed of, for example, a ceramic having an equivalent coefficient of linear thermal expansion to the coefficient of linear thermal expansion of the wafer (see, for example, Japanese Patent Application Laid-Open Nos. 231019/1995 and 5666/1996, etc.). In such a probe member, as means for fixing the anisotropically conductive elastomer sheet to the circuit board for inspection, a means that peripheral portions of the anisotropically conductive elastomer sheet are mechanically fixed by, for example, screws or the like, a means that it is fixed with an adhesive or the like, and the like are considered.
However, in the means that the peripheral portions of the anisotropically conductive elastomer sheet are fixed by the screws or the like, it is extremely difficult to prevent positional deviation between the electrodes to be inspected in the wafer and the conductive parts in the anisotropically conductive elastomer sheet for the same reasons as the means of fixing to the frame plate as described above.
On the other hand, in the means of fixing with the adhesive, it is necessary to apply the adhesive only to the insulating part in the anisotropically conductive elastomer sheet in order to surely achieve electrical connection to the circuit board for inspection. Since the anisotropically conductive elastomer sheet used in the WLBI test is small in the arrangement pitch of the conductive parts, and a clearance between adjacent conductive parts is small, however, it is extremely difficult in fact to do so. In the means of fixing with the adhesive also, it is impossible to replace only the anisotropically conductive elastomer sheet with a new one when the anisotropically conductive elastomer sheet suffers from trouble, and so it is necessary to replace the whole probe member including the circuit board for inspection. As a result, increase in inspection cost is incurred.
When the probe test or WLBI test of a wafer is conducted by using the anisotropically conductive connector, the anisotropically conductive elastomer sheet thereof is held with pressure by the wafer that is an object of inspection and the circuit board for inspection, whereby the conductive parts formed by an elastic polymeric substance are deformed under pressure, thereby achieving electrical connection between electrodes to be inspected of the wafer, which is the object of inspection, and the inspection electrodes of the circuit board for inspection.
In the electrical connection between electrodes to be inspected of the wafer, which is the object of inspection, and the inspection electrodes of the circuit board for inspection, when the projected height of the respective electrodes to be inspected and the projected height of the respective inspection electrodes vary, pressurizing force applied to the respective conductive parts in the anisotropically conductive connector varies, whereby, in the respective conductive parts, the degree of deformation under pressure varies according to the intensity of the pressurizing force applied to the respective conductive parts, so that the electrical connection between the electrodes to be inspected and the inspection electrodes of the circuit board for inspection is achieved. Such function of the anisotropically conductive connector will hereinafter be referred to as “level difference-absorbing ability”.
Since the level difference-absorbing ability of the anisotropically conductive connector is created by the tendency to deform under pressure that the elastic polymeric substance forming the conductive parts has, greater pressurizing force is required for achieving electrical connection to all the electrodes to be inspected as a difference in projected height between the respective electrodes to be inspected and a difference in projected height between the respective inspection electrodes become greater. When the difference in projected height between the respective electrodes to be inspected and the difference in projected height between the respective inspection electrodes are too great, it is difficult to achieve the electrical connection to all the electrodes to be inspected.
The projected height of individual conductive parts formed by an elastic polymeric substance in an anisotropically conductive connector may vary in some cases.
Since an anisotropically conductive connector great in the difference in projected height between respective conductive parts has low level difference-absorbing ability, considerably great pressurizing force is required for achieving electrical connection, by such anisotropically conductive connector, to all electrodes to be inspected of a wafer that is an object of inspection, or difficulty is encountered on the achievement of electrical connection to all the electrodes to be inspected.
When a wafer that is an object of inspection is of large size of, for example, at least 8 inches in diameter, and the number of electrodes to be inspected formed thereon is, for example, at least 5,000, particularly at least 10,000, an anisotropically conductive connector used in the inspection of such a wafer is required to have an extremely great number of conductive parts. Therefore, the anisotropically conductive connector for inspecting such a wafer is pressurized by great pressurizing force for achieving electrical connection to all the electrodes to be inspected upon inspection. In order to achieve the electrical connection to all the electrodes to be inspected, still greater pressurizing force is required as a difference in projected height between the respective electrodes to be inspected and a difference in projected height between the respective inspection electrodes become greater.
As a probe member for wafer inspection, is known that obtained by arranging an anisotropically conductive connector and a sheet-like connector in this order on a circuit board for inspection. The sheet-like connector in this probe member have projected surface electrodes (bumps) formed by plating, and the surface electrodes are brought into contact with respective electrodes to be inspected, thereby achieving electrical connection to the electrodes to be inspected. Since the surface electrodes in such a sheet-like connector vary in the projected height thereof, and the difference in projected height between the respective surface electrodes is comparatively great, the level difference-absorbing ability of the anisotropically conductive connector becomes extremely important in the probe member having such a sheet-like connector.
In the inspection of a wafer having a large area of 8 inches or greater in diameter, in which the number of electrodes to be inspected is extremely great, a large-sized mechanism is required as a pressurizing mechanism installed in a wafer inspection apparatus for inspecting the wafer when the pressurizing force required for achieving the electrical connection to all the electrodes to be inspected becomes great. As a result, the whole wafer inspection apparatus becomes a large scale. Therefore, it is desired that the probe member used in the wafer inspection apparatus can achieve electrical inspection to all the electrodes to be inspected by small pressurizing force. Accordingly, it is desired that the anisotropically conductive connector used in such a probe member be little in the difference in projected height between the respective conductive parts and high in the level difference-absorbing ability and can achieve the electrical inspection to all the electrodes to be inspected by small pressurizing force.